The redefined environmental standards are officially the main reason for the latest renovations. The brand new claddings and interior fittings would be significantly more energy efficient than older ones. So although some older buildings yet insteresting should be preserved, businesses generally don't want to stay in obsolete towers. They want the latest thing to cut their energy bills and say - see how green we are! the building we live in fulfills the commitment to save Earth.

Besides, the district wasn't aging well as too many buildings of the 60s-70s in Paris look bad nowadays. So all operations going on are to bring more modernity and dynamism. It's either being on the move or declining, an easy choice to make.

__________________
psst... A new command I give you: Love one another. As I have loved you, so you must love one another. (John 13:34)
I like bass. Give me some.

Within the neighborhood of Carpe Diem and D2 currently U/C and of Eqho being heavily restructured (above in this thread), the refurbishment of Chartis (also called CB15 or AIG), which is to begin in early 2013, will complete the renovation of that part of the district I believe. At least regarding existing highrise structures. There are still some post-war low/mid-rise things around, along the esplanade, that I personally would prefer demolished or seriously restructured.
This is how Chartis would look:

A bit the same as those white columns of the facade seem to stay, but they would completely change the glass and then call it Tour Blanche, that simply means white tower. Chartis was one of those first, smaller high-rises built in la Défense during the 60s, as well as its close neighbor Europe being partly refurbished too, but of which the original facade won't change.

These pics are under Icade's copyright, but Icade is also the developer so I hope they won't mind if we promote their project on here.
To me, it looks as if some kind of cheap crappy old style you sometimes see in some 60's-70's industrial areas had become shiny good quality.
I actually like their thing, when the sky is blue especially.

__________________
psst... A new command I give you: Love one another. As I have loved you, so you must love one another. (John 13:34)
I like bass. Give me some.

Currently under construction, the arena will become the residence of local rugby club Racing 92 upon completion later this year. With a seating capacity of 32,000 during rugby games, the structure was designed by French architecture firm Atelier Christian de Portzamparc and contributes to the urban redevelopment scheme overseen by the government-operated EPADESA. The arena will be equipped with artificial turf, 22 bars and restaurants, 100 private booths, a 2,000-square-metre screen for simultaneous broadcasting, and be built according to the High Environmental Quality regulations, a standard for green building in France. Arena 92, on the right of the image, will be complete by then end of 2016, image by Flickr user Guilhem Vellut